In conventional photographic image forming processes, photographic solutions such as developer, fixer and bleach-fixer are usually employed. In order to remove complications using these solutions, a silver salt diffusion transfer method, a wet color diffusion transfer method (so-called instant color photography) and a heat development method are put into practical use.
In the heat development method, in which development is carried out by applying heat, a method giving a white and black image or a color image is known, and an image transfer type heat developable light sensitive material, in which a developed image is transferred to an image receiving layer, is also well known.
The heat developable light sensitive material usually comprises a support, a binder, a light sensitive silver halide emulsion, a reducing agent, optionally a dye providing material, an organic silver salt or other photographic additives. In the image transfer type heat developable light sensitive material, a light sensitive material and an image receiving layer receiving silver or a dye are formed as one body or separately.
In order to obtain a high contrast image in a method employing such a heat developable light sensitive material, a method was examined in which pH is elevated in a development and/or image transfer process. For example, Japanese Patent O.P.I. Publication Nos. 56-130745/1981 and 56-132332/1981 disclose a method in which at least one of a heat developable light sensitive material and an image receiving layer contains an alkali providing material. However, this method tends to elevate pH in a coating solution containing an alkali component, and affects physical properties of a hydrophilic binder, resulting in coating faults. Further, the image formed is likely to have uneven density in which image density is extraordinarily lower (so-called white spots) or higher (so-called black spots) than the neighboring image density. The alkali containing coating solution, when neutralized with an acidic component to maintain the physical properties of the hydrophilic binder, does not sufficiently show desired pH increasing effects.
British Patent No. 998949, U.S. Pat. Nos. 3,220,846 and 3,523,795, Japanese Patent O.P.I. Publication Nos. 50-22625/1975, 59-168440/1984, 59-168441/1984, 59-180537/1984, 60-237443/1985, 61-32844/1986, 61-36743/1986, 61-52639/1986, 61-51139/1986, 61-51140/1986, 61-52638/1986, 61-53631/1986, 61-53634/1986, 61-53635/1986, 61-53636/1986, 61-53637/1986, 61-53638/1986, 61-53639/1986, 61-53640/1986, 61-55644/1986, 61-55645/1986, 61-55646/1986, 61-219950/1986 and 61-251840/1986 disclose a method in which a heat developable light sensitive material and/or an image receiving layer contains an alkali providing material (an alkali precursor) releasing or forming an alkali component on application of heat. In this method, however, the heat developable light sensitive material or image receiving layer containing an alkali precursor is likely to be affected by atmospheric conditions. As a result, there are problems such that the materials tend to have a sticky surface, the image formed has image unevenness, and the precursor decomposes, resulting in deterioration of photographic properties.
U.S. Pat. No. 3,260,598 discloses an image forming method employing a process in which pH increases on reaction during development of a sparingly water-soluble metal hydroxide with a sodium or potassium salt (hereinafter referred to also as a complex forming compound) of a ligand which is capable of coordinating with the metal contained in the sparingly water-soluble metal hydroxide. This method can prevent deterioration of physical layer properties or photographic properties during storage, since the sparingly water-soluble metal hydroxide and complex forming compound are present separately before the image forming reaction. However, this method, when applied to heat development, does not give a satisfactory contrast image.
Japanese Patent O.P.I. Publication No. 62-187847/1987 discloses a method which produces an alkali during the complex forming reaction of a heterocyclic carboxylic acid salt having a specific structure, represented by picolinic acid guanidine salt, with a sparingly water-soluble metal compound such as zinc hydroxide. However, when the specific heterocyclic carboxylic acid salt, represented by picolinic acid guanidine salt, is added to a layer containing a hydrophilic binder, the layer tends to have a sticky surface under high humidity, and there is also a problem in view of physical layer properties.
Japanese Patent O.P.I. Publication No. 62-174745/1987 discloses a method which produces an alkali on reaction of a sparingly water-soluble metal compound with a neutral water soluble compound which is capable of forming a still less water-soluble metal compound on reaction with a metal ion contained in the sparingly water-soluble metal compound. In this method, a sparingly water-soluble salt such as silver carbonate or calcium hydroxide and a water-soluble salt such as a water soluble fluoride or iodide are employed which has a great influence on photographic properties. Since barium carbonate has a great tendency to form a sparingly water-soluble salt on reaction with a sulfonic acid, there is a problem that the carbonate can not be used in combination with pH adjusting agents such as surfuric acid or photographic agents having a sulfonate group.
The present inventors have proposed in Japanese Patent Application No. 5-316902/1993 that a method employing an aminopolycarboxylic acid derivative whereby improved physical layer properties and a high contrast image can be obtained. In this method, however, gloss of the image plane and peelability after development of a light sensitive material from an image receiving layer are not always satisfactory, and further improvement has been desired.